1. Field of the Invention
The present invention relates to a rotary coupled transmission line cell which generates standard electromagnetic waves (plane waves, magnetic waves and electric waves) needed for measuring the electromagnetic wave susceptibility (EMS), for measuring the electromagnetic wave interference (EMI) and for calibrating the probe.
2. Description of the Prior Art
The existing TEM (transverse electromagnetic) cell includes: Crawford TEM cell, GTEM (Giga-Htz TEM) cell, TTEM (triple TEM) cell, WTEM (wire TEM) cell, improved GTEM cell, automatic measuring TEM cell and the like. They can be classified into two types. That is, one of them is the one terminal TEM cell in which the input/output terminals are located on one face, and this category includes GTEM cell, WTEM cell, TTEM cell, and improved GTEM cell. The other is two-terminal TEM cell in which the input/output terminals are located on both faces, and this category includes Crawford TEM cell, asymmetric TEM cell, automatic measuring TEM cell, and 6-ports TEM cell.
All of them are adapted to measure electromagnetic wave interference, to measure electromagnetic susceptibility, and to calibrate antenna. The TEM cells belonging to the former class are capable of testing only far fields, while those belonging to the latter are capable of testing not only far fields but also near fields. Particularly, during the measurement of the electromagnetic interference, the former class is capable of measuring the dipole moments of the crossing components, while the latter class is not capable. Thus they are different. Particularly among the tow-terminal TEM cells, those which can adjust the polarization include: assembling type cylindrical TEM cell, automatic measuring TEM cell, 6-ports TEM cell, 8-ports variable impedance EM generating apparatus, and rotary cylindrical TEM cell.
Among them, except assembling type cylindrical TEM cell and rotary cylindrical TEM cell, all of them are capable of generating the standard electromagnetic waves at particular polarizations (45 degrees, 90 degrees, and 135 degrees), but are impossible to generate the standard electromagnetic waves having arbitrary polarizations. The technique of forming arbitrary polarizations is very important for measuring the electromagnetic susceptibility and the electromagnetic interference.
Rotary cylindrical TEM cell is that which has improved the narrow polarization range of the assembling type cylindrical TEM cell, the problem of the small uniform area for the test object, and the accuracy of the angle adjustment.
However, there is disposed one internal conductor in this TEM cell, and therefore, has to have a two-port structure. Therefore, as shown in FIG. 5a, the improvement of the internal electric field uniformity is limited. Further, in the case where the standard electromagnetic waves having arbitrary impedances are to be generated, there are produced circulating transmission waves, with the result that the accuracy is degraded.